The present invention relates to an optical storage medium for recording and reproducing information using a laser beam and an optical storage apparatus.
Recently, attention is being paid to disk and card/tape types of optical storage media, such as phase changing and magneto-optical type media. Particularly, there is an interest in optical disks with higher recording capacities than the currently available floppy disks, and in hard disks using recording pits of the sub-micron order positioned on the medium. Such magneto-optical disks utilize rare earth-transition metal based materials, and can be rewritten a hundred thousand times, or more. Therefore, there is an interest in further development of such magneto-optical disks.
A 3.5 inch optical disk with a recording capacity of either 540 MB or 640 MB on only one side has recently been developed. For comparison purposes, the recording capacity of one side of a conventional 3.5 inch floppy disk is about 1 MB. Thus, one side of an optical disk has the recording capacity equal to that of 540 or 640 floppy disks. Accordingly, it goes without saying that an optical disk is a rewritable storage medium having a very high recording density.
However, even such high recording densities must further be increased in order to satisfy the requirements of the multimedia era, both now and in future. Therefore, a larger number of marks should be recorded on the medium in order to increase the recording density. For this purpose, the marks currently used should be reduced in size, and the interval between marks should also be decreased.
When attempting to raise the recording density with the method explained above, one option is to attempt to shorten the wavelength of the laser beam from its current value of 685 nm. However, there is another option in which the pit size is reduced, while still maintaining the current wavelength of 685 nm. Under this option, it is possible during recording to form marks which are smaller than the beam diameter by controlling the power of laser beam. But, during reproducing, when a mark smaller than the beam diameter is reproduced, crosstalk to the neighboring marks increases. In the worst case, the neighboring mark is included within the reproducing beam. Practically speaking, it is very difficult to overcome this crosstalk problem under normal use conditions.
However, two methods of reproducing marks which are smaller than the beam diameter in the current wavelength of 685 nm are two different types of magnetically induced super-resolution (MSR) techniques which can be classified as a FAD (front aperture detection) system and a RAD (rear aperture detection) system.
More particularly, in the RAD system, an initialization is performed, as shown in FIG. 17(B), using an initializing magnet 232 to set the magnetizing direction of the reproducing layer 216 to a constant direction. The reading operation is conducted with a reproducing laser (whose power is slightly increased during this operation), a mask 236 (for allowing the initial magnetizing information of the reproducing layer 216 to be retained) and an aperture 238 (for allowing the heat of the laser spot 234 to transfer the magnetizing information of the recording layer 220 to the reproducing layer 216 after erasing the initial magnetizing information). The mask 236 and the aperture 238 result from the temperature distribution of the spot 234. The magnetizing information of the recording layer 220 transferred to the reproducing layer 216 is converted to an optical signal by means of the magneto-optical effect (e.g., the Kerr effect or the Faraday effect) for data reproduction.
In this case, although the mark 228 of the track 214 currently being read by the laser beam has been transferred to the reproducing layer 216, the mark 230 intended to be read next is not transferred due to the formation of the mask 236. Thus, even when the recording mark is smaller than the laser spot 234, crosstalk is not generated, and marks smaller than the beam diameter can be reproduced. Moreover, when this magnetically induced super resolution technique is used, since the area outside of the reproducing area of the recording layer 220 is masked by the initialized reproducing layer 216, mark interference from neighboring marks is not generated, and the mark interval can be reduced. Accordingly, since crosstalk from the neighboring tracks can also be suppressed, the track pitch can also be reduced, and high density recording/reproducing can be obtained even when using the current wavelength of 685 nm.
Japanese Published Unexamined Patent Application Nos. HEI 7-244877, HEI 9-147436 and HEI 10-134429 disclose some of the details of the principles of magnetically induced super resolution techniques, examples of rare earth-transition metal based film material of magneto-optical recording medium layers consisting of a reproducing layer, a switch layer (an intermediate layer) and a recording layer; and examples of magneto-optical storage medium manufacturing methods.
However, optical memory devices for driving optical storage mediums for high density recording have a problem in that adequate recording operations cannot be realized if the laser power for the recording operation is not strictly controlled.
Moreover, another problem that has also been found is that the sensitivity of the storage medium changes depending on the number of write and erase operations performed, which results in imperfect control of the laser power during recording, which thereby increases the rate of recording errors.
The present invention has been proposed, considering the problems of the related art explained above, and it is therefore an object of the present invention to provide an optical storage medium, a method of processing that medium, and an optical storage medium processing apparatus which enables highly reliable high density recording by strictly controlling the laser power of the recording operation in each area of an optical storage medium that is not effected by the number of write and erase operations.
The present invention is characterized in that a high power process is repeatedly performed upon an optical storage medium. In this high power process, the power of the optical beam is increased to a higher power than that used for recording or erasing, and the beam is radiated upon a power adjusting area of the optical storage medium. This power adjusting area is used, at least in part, to adjust the power of the optical beam.
Moreover, the present invention also relates to an optical storage medium processing apparatus for accessing an optical storage medium by radiating thereto an optical beam. This apparatus includes an optical head for radiating an optical beam of a predetermined power to a predetermined position of the optical storage medium; and a high power process controller for positioning the optical head to direct the optical beam to a power adjusting area. The high power process controller is also used for controlling the power of the optical beam to be a power that is higher than that used for recording or erasing, to thereby control a high power process in which the high power optical beam is radiated upon the power adjusting area.
With the present invention, the sensitivity characteristic of the power adjusting area of the medium at its initial condition (i.e., during the period immediately after the manufacture of the optical storage medium) may be changed to a sensitivity characteristic of a saturated condition after repetition of write and erase operations a plurality of times. Namely, in this saturated condition, even after the write and erase operations are repeated, sensitivity shifts (i.e., variations of the optimum recording power) do not occur, and the optimum recording power for the medium can precisely be controlled.
Naturally, it is better to conduct the high power process upon the entire medium, but processing times as long as several thousand minutes may be required for performing high power processing upon the entire medium. Therefore, in the present invention, high power processing is performed only to the power adjusting area. Because the power adjusting area is used to adjust the power of the optical beam power, and because the present invention eliminates sensitivity shifts, precise control of the optical power can be obtained.
Moreover, when the medium substrate is formed of a resin such as polycarbonate, if the medium as a whole (or if all of the tracks) are heated for a long period of time, cracks may be generated, and these cracks disable successive use of the medium. However, the present invention provides that generation of cracks can be prevented by performing the high power process only to the necessary area.
The present apparatus is also characterized in that the optical beam is radiated at a higher power than ordinary power, and simultaneously a magnetic field of a predetermined direction is also applied to the medium. This predetermined direction of the magnetic field is identical to the erasing direction. Thus, in the present invention, high power erasing is performed by radiating the optical beam upon the optical storage medium in the high power while applying thereto a magnetic field in the erasing direction.
Therefore, since the magneto-optical medium is heated with an optical beam while a magnetic field is being applied thereto, the magnetic condition of the magnetic film of the medium is changed to the recording or the erasing condition, and when such changes are repeated multiple times, the magnetizing condition can then be shifted to the saturated condition.
In addition, the present invention is also characterized in that the high power process can be performed during the process of certifying the optical storage medium. The optical storage medium is certified, to initially write the information, by detecting defects of medium, and then by writing defect list information (PDL) to the medium. At the time of performing this process, when the high power process is performed, such a write process is conducted with precise control of the optimum recording power, and thereby highly reliable recording can be realized.
In addition, the present invention is also characterized in that the rotational frequency of the optical storage medium may be set, while conducting the high power process, to a value that is lower than the usual rotational frequency. Therefore, the period of time that each section of the medium is heated by the beam is increased, and the beam power does not need to be raised as high. When the desired medium heating temperature (which is a temperature higher than the Curie point of the recording layer) is attained, the beam power may be then set to be identical to that used for ordinary recording and erasing, depending on rotational frequency.
The present invention is also characterized in that the off-track detecting function is at least partially disabled during the high power process. Therefore, the accuracy for detecting off-track errors during the high power process is lowered to prevent interruptions in the process due to minute errors, and to shorten the processing time, because detecting accuracy is not critical during this period since user data is not being recorded to the data area.
The present invention also relates to an optical storage medium processing method that includes the steps of radiating an optical beam upon an optical medium at a power that is higher than the power used for recording or erasing; and repeatedly impressing a high power magnetic field upon the medium in order to impress the magnetic field of the medium into a predetermined direction.
Therefore, the sensitivity characteristic of the medium in its initial condition (immediately after its manufacture) can be changed to that of a saturated condition after the write and erase operations are repeated for a plural number of times. Particularly, since the medium is heated with an optical beam while a magnetic field is being applied thereto, the magnetic condition of magnetic film of the medium can be changed to the recording or the erasing condition, and if such changes are repeated enough, the magnetizing condition can surely be shifted to a saturated condition.
The high power process of the present invention may be executed to all tracks of the medium, or it may be executed only to areas that are assured of a higher recording frequency, such as the power adjusting area or the like.
The optical storage medium processing apparatus of the present invention may also be characterized by a power adjustment processor for determining a preliminary optimum recording power to be used for determining an appropriate power for recording information to an information recording area of the optical storage medium, where this determination is made by recording to a power adjusting area of the optical storage medium prior to recording said information, and wherein the power adjusting area has undergone a high power process; and a power processor for obtaining the optimum recording power for the recording of information to the information recording area, where the optimum recording power is attained by compensating the preliminary optimum recording power obtained by the power adjustment processor with a predetermined amount of sensitivity compensation.
Therefore, the optimum recording power of the information recording area can be obtained, and highly reliable recording can also be realized by compensating the preliminary optimum recording power obtained by the test write for power adjustment upon the storage medium to which the high power process has been conducted in the power adjusting area (test area), with the sensitivity compensation amount determined depending upon the medium sensitivity characteristic and the temperature characteristic of the information recording area.
In addition, the sensitivity compensation amount can be determined so that the sensitivity shift is within the range of the optimum recording power in the saturated condition, and so that it is also within the range of the optimum recording power in the initial condition, with the power satisfying the predetermined conditions becoming identical to the optimum recording power in the information recording area.
Since high power processing is performed to the power adjusting area, the sensitivity shift of such area is saturated. The information recording area changes its sensitivity shift from the initial condition to the saturated condition depending on its application frequency, and the optimum recording power also fluctuates during this change in conditions. Therefore, in the present invention, the optimum recording power of the information recording area is determined so that sufficient power is obtained for both types of areas, i.e., areas where the sensitivity shift is in the initial condition and areas where it is in the saturated condition.
Because the optimum recording power under the initial condition and the saturated condition are measured respectively, thereby any deviation from the optimum recording power of the power adjusting area can be obtained. This deviation is predetermined as the sensitivity compensation amount. Therefore, the optimum power of the information recording area can easily be obtained by only conducting a write test.
Moreover, it is also possible to change the sensitivity compensation amount depending upon the environmental temperature in order to precisely control the sensitivity compensation amount. In addition, it is also possible to change the sensitivity compensation amount for each zone of the optical storage medium. Moreover, for this purpose, the sensitivity compensation amount can be also changed by adding or subtracting a constant amount during the rewriting operation when a recording error is generated.
The present invention also relates to an optical storage medium capable of having information repeatedly recorded thereon by receiving radiation from an optical beam, where that medium includes a plurality of zones dividing the medium, wherein each zone has a Curie point, and a heating process area in each of the zones, wherein a heating process conducted at a temperature that is higher than the Curie point of the associated zone has been performed upon each heating process area. Each zone is formed of a plurality of areas which are divided, for access management, in the radius direction of the optical storage medium, and are provided for control of zone CAV and zone CLV.
In addition, it is also a characteristic of the present invention that a control area is provided in the optical storage medium to record information indicating that the high power process has been conducted. Therefore, the high power process will not be unnecessarily performed over and over again.